Adjustable voltage constant current light emitting diode (LED) driver for automotive headlights

Abstract

Various embodiments include a voltage adjusting block (VAB) coupled to a light emitting diode (LED) string. The VAB includes a first switch having a first lead connected to a voltage input, and having a second lead, the first switch having a controllable duty cycle, a first diode having a cathode connected to the second lead of the first switch, and having an anode, a first inductor having a first lead connected to the cathode of the first diode, and having a second lead, and a first capacitor having a first lead connected to the anode of the first diode and having a second lead connected to the second lead of the first inductor. The VAB may provide a variable voltage across the anode of the first diode and the second lead of the first capacitor dependent upon a number of LEDs in the LED string being turned on.

What is claimed is: 
     
       1. A circuit comprising:
 a voltage adjusting block (VAB) coupled to a light emitting diode (LED) string, comprising:
 a first switch having a first lead connected to a voltage input, and having a second lead, the first switch having a controllable duty cycle; 
 a first diode having a cathode connected to the second lead of the first switch, and having an anode; 
 a first inductor having a first lead connected to the cathode of the first diode, and having a second lead; and 
 a first capacitor having a first lead connected to the anode of the first diode and having a second lead connected to the second lead of the first inductor; and 
 
 wherein the VAB provides a variable voltage across the anode of the first diode and the second lead of the first capacitor dependent upon a number of LEDs in the LED string being turned on; 
 a LED string controller having a first input connected to the anode of the first diode, having a second input, and having a plurality of outputs controlling operation of the LED string; 
 a constant current block (CCB) having a first input, having a second input connected to the second lead of the first capacitor and having an output connected to the second input of the LED string controller; and 
 a battery having a first lead connected to the input of the CCB, and having a second lead connected to the second input of the CCB. 
 
     
     
       2. The circuit of  claim 1 , further comprising an electromagnetic interference (EMI) filter having a first connection to the first lead of the battery and having a second connection to the second lead of the battery. 
     
     
       3. The circuit of  claim 1 , wherein:
 the LED string comprises a plurality of LEDs connected in series; 
 an anode of a first LED of the plurality of LEDs is connected to the second input of the LED string controller; 
 a cathode of a last LED of the plurality of LEDs is connected to the first input of the LED string controller; and 
 the LED string controller further comprises:
 a plurality of bypass switches, wherein each bypass switch is connected across one of the plurality of LEDs; and 
 a controller having an input and a plurality of outputs, wherein each bypass switch of the plurality of bypass switches is controlled by an output of the plurality of outputs of the controller. 
 
 
     
     
       4. The circuit of  claim 3 , wherein a first bypass switch in the plurality of bypass switches comprises:
 a switch diode having a cathode connected to a first lead of the first bypass switch and having an anode connected to a second lead of the first bypass switch; and 
 a switch capacitor having a first lead connected to the first lead of the first bypass switch and having a second lead connected to a second lead of the first bypass switch. 
 
     
     
       5. The circuit of  claim 1 , wherein the CCB comprises:
 a second switch having a first lead connected to the first lead of the battery, and having a second lead; 
 a second diode having a cathode connected to the second lead of the second switch, and 
 having an anode connected to the second lead of the battery; and 
 a second inductor having a first lead connected to the cathode of the second diode, and having a second lead connected to the second input of the LED string controller. 
 
     
     
       6. The circuit of  claim 5 , further comprising:
 a second switch diode having a cathode connected to the first lead of the second switch and having an anode connected to the second lead of the second switch; and 
 a second switch capacitor having a first lead connected to the first lead of the second switch and having a second lead connected to the second lead of the second switch. 
 
     
     
       7. The circuit of  claim 1 , wherein the VAB further comprises a controller that is configured to adaptively adjust a voltage output of the VAB by altering a duty ratio of the first switch such that an voltage output of the CCB is kept approximately constant. 
     
     
       8. The circuit of  claim 1 , further comprising:
 a first switch diode having a cathode connected to the first lead of the first switch and having an anode connected to the second lead of the first switch; and 
 a first switch capacitor having a first lead connected to the first lead of the first switch and having a second lead connected to the second lead of the first switch. 
 
     
     
       9. A circuit comprising:
 a voltage adjusting block (VAB) coupled to a light emitting diode (LED) string, comprising:
 a first switch having a first lead connected to a voltage input, and having a second lead, the first switch having a controllable duty cycle; 
 a first diode having a cathode connected to the second lead of the first switch, and having an anode; 
 a first inductor having a first lead connected to the cathode of the first diode, and having a second lead; and 
 a first capacitor having a first lead connected to the anode of the first diode and having a second lead connected to the second lead of the first inductor; and 
 
 wherein the VAB provides a variable voltage across the anode of the first diode and the second lead of the first capacitor dependent upon a number of LEDs in the LED string being turned on, and the LEDs in the LED string are turned on one at a time. 
 
     
     
       10. A circuit comprising:
 a voltage adjusting block (VAB) coupled to a light emitting diode (LED) string, comprising:
 a first switch having a first lead and a second lead, the first switch having a controllable duty cycle; 
 a first diode having a cathode, and having an anode connected to the first lead of first switch; 
 a first inductor having a first lead connected to the anode of the first diode, and having a second lead connected to an input voltage; and 
 a first capacitor having a first lead connected to the cathode of the first diode and having a second lead connected to the second lead of the first switch; 
 
 wherein the VAB provides a variable voltage across the first capacitor dependent upon a number of LEDs in the LED string being turned on; 
 a constant current block (CCB) having a first input connected to the cathode of the first diode, having a second input connected to the second lead of the first capacitor and having an output; 
 an LED string controller having an input connected to the output of the CCB and having an output connected to the second lead of the first switch; and 
 a battery having a first lead connected to the second lead of the first inductor, and a second lead connected to the second lead of the first switch. 
 
     
     
       11. The circuit of  claim 10 , further comprising an electromagnetic interference (EMI) filter having a first connection to the first lead of the battery and having a second connection to the second lead of the battery. 
     
     
       12. The circuit of  claim 10 , wherein:
 the LED string comprises a plurality of LEDs connected in series; 
 an anode of a first LED of the plurality of LEDs is connected to a second lead of a second inductor in the CCB; 
 a cathode of a last LED of the plurality of LEDs is connected to the second lead of the battery; and 
 the LED string controller comprises:
 a plurality of bypass switches, wherein each bypass switch is connected across one of the plurality of LEDs; and 
 a controller having an input and a plurality of outputs, wherein each bypass switch of the plurality of bypass switches is controlled by an output of the plurality of outputs of the controller. 
 
 
     
     
       13. The circuit of  claim 12 , wherein a first bypass switch in the plurality of bypass switches comprises:
 a switch diode having a cathode connected to a first lead of the first bypass switch and having an anode connected to a second lead of the first bypass switch; and 
 a switch capacitor having a first lead connected to the first lead of the first bypass switch and having a second lead connected to a second lead of the first bypass switch. 
 
     
     
       14. The circuit of  claim 10 , wherein the CCB comprises:
 a second switch having a first lead connected to cathode of the first diode, and having a second lead; 
 a second diode having a cathode connected to the second lead of the second switch, and having an anode connected to the second lead of the battery; and 
 a second inductor having a first lead connected to the cathode of the second diode, and having a second lead connected to the anode of the first LED of the plurality of LEDs. 
 
     
     
       15. The circuit of  claim 14 , further comprising:
 a second switch diode having a cathode connected to the first lead of the second switch and having an anode connected to the second lead of the second switch; and 
 a second switch capacitor having a first lead connected to the first lead of the second switch and having a second lead connected to the second lead of the second switch. 
 
     
     
       16. The circuit of  claim 10 , wherein the VAB further comprises a controller that is configured to adaptively adjust a voltage output of the VAB by altering a duty ratio of the first switch such that an voltage output of the CCB is kept approximately constant. 
     
     
       17. The circuit of  claim 10 , further comprising:
 a first switch diode having a cathode connected to the first lead of the first switch and having an anode connected to the second lead of the first switch; and 
 a first switch capacitor having a first lead connected to the first lead of the first switch and having a second lead connected to the second lead of the first switch. 
 
     
     
       18. A circuit comprising:
 a voltage adjusting block (VAB) coupled to a light emitting diode (LED) string, comprising:
 a first switch having a first lead and a second lead, the first switch having a controllable duty cycle; 
 a first diode having a cathode, and having an anode connected to the first lead of first switch; 
 a first inductor having a first lead connected to the anode of the first diode, and having a second lead connected to an input voltage; and 
 a first capacitor having a first lead connected to the cathode of the first diode and having a second lead connected to the second lead of the first switch; 
 
 wherein the VAB provides a variable voltage across the first capacitor dependent upon a number of LEDs in the LED string being turned on and the LEDs in the LED string are turned on one at a time.